Modification of PCBM Crystallization via Incorporation of C₆₀ in Polymer/Fullerene Solar Cells

Abstract The morphological effects of the incorporation of C₆₀ into blended thin‐films of poly(3‐hexylthiophene) and [6,6]‐phenyl C₆₁ butyric acid methyl ester (PCBM) are investigated. The results show that addition of C₆₀ readily alters the growth‐rate and morphology of PCBM crystallites under different environmental conditions. The effect of C₆₀ on the growth of large PCBM crystallites is thoroughly characterized using optical microscopy, electron microscopy and UV‐visible absorption spectroscopy. Results show that C₆₀ incorporation modifies fullerene aggregation and crystallization and greatly reduces the average crystallite size at C₆₀ loadings of ≈50 wt% in the fullerene phase. Organic field‐effect transistors (OFETs) are prepared to evaluate the electron mobility of PCBM/C₆₀ films and organic solar cells (OSCs) are fabricated from mixed‐fullerene active layers to evaluate their performance. It is demonstrated that the use of fullerene mixtures in organic electronic applications is a viable approach to produce more stable devices and to control the growth of micrometer‐sized fullerene crystals.